docs: def _highlight(html):
      """Syntax-highlights HTML-rendered Markdown.
  
      Plucks sections to highlight that conform the the GitHub fenced code info
      string as defined at https://github.github.com/gfm/#info-string.
  
      Args:
          html (str): The rendered HTML.
  
      Returns:
          str: The HTML with Pygments syntax highlighting applied to all code
              blocks.
      """
  
      formatter = pygments.formatters.HtmlFormatter(nowrap=True)
  
      code_expr = re.compile(
          r'<pre><code class="language-(?P<lang>.+?)">(?P<code>.+?)'
          r'</code></pre>', re.DOTALL)
  
      def replacer(match):
          try:
              lang = match.group('lang')
              lang = _LANG_ALIASES.get(lang, lang)
              lexer = pygments.lexers.get_lexer_by_name(lang)
          except ValueError:
              lexer = pygments.lexers.TextLexer()
  
          code = match.group('code')
  
          # Decode html entities in the code. cmark tries to be helpful and
          # translate '"' to '&quot;', but it confuses pygments. Pygments will
          # escape any html entities when re-writing the code, and we run
          # everything through bleach after.
          code = html_parser.HTMLParser().unescape(code)
  
          highlighted = pygments.highlight(code, lexer, formatter)
  
          return '<pre>{}</pre>'.format(highlighted)
  
      result = code_expr.sub(replacer, html)
  
      return result